Casting process for aluminium alloys

ABSTRACT

A process for manufacturing an aluminum-based alloy sheet directly from a molten aluminum-based alloy is described. In a continuous caster, such as a belt-caster, and directly from the molten aluminum-based alloy, a substantially solid and substantially thin aluminum-based alloy strip, thinner than about 10 mm, is continuously cast and simultaneously cooled with a compression force on the solidifying aluminum-based alloy in a range of about 2 to about 3000 pounds per linear inch of alloy strip width. The substantially solid aluminum-based alloy strip can then be rolled, so as to obtain the aluminum-based alloy sheet. The process can include pulse heating the aluminum-based allowed sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35USC § 119(e) of U.S. provisional patent applications 63/110,568 filed Nov. 6, 2020 and 63/262,448 filed Oct. 13, 2021, the specifications of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a casting process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy. More particularly, it relates to a casting process wherein an aluminum-based alloy strip thinner than about 10 mm is cast and then can be rolled into an aluminum-based alloy sheet.

BACKGROUND

Some of the conventional processes for manufacturing an aluminum-based alloy sheet for use in commercial applications, such as auto panels, reinforcements, beverage containers and aerospace applications, employ batch processes which include an extensive sequence of separate steps. Typically, a large solid aluminum-based alloy is cast to a thickness of up to about 50 centimeters, water-cooled to ambient temperature, and then stored for later use. When an aluminum-based alloy ingot is needed for further processing, it is first scalped to remove surface defects from the rolling faces. Then it is preheated to a specific temperature, requiring a ramp-up hold ramp-down cycle of 20 to 30 hours, which is termed homogenization. The pre-heated aluminum-based alloy ingot is then cooled to a lower temperature for hot rolling. Several passes are needed to reduce the thickness of the aluminum-based alloy ingot to the required range for cold rolling. Additionally, an intermediate anneal is typically carried out on the coil. The resulting aluminum-based alloy strip is then cold-rolled to the desired gauge and coiled to obtain the aluminum-based alloy sheet and may be subsequently heated to an elevated temperature (tempered) to meet a specific mechanical property such as yield strength, tensile elongation, etc. To produce a heat-treatable aluminum-based alloy sheet that will meet specific metallurgical requirements, the aluminum-based alloy coiled sheet may also be subjected to a separate heat treatment stage, typically in a continuous heat-treatment line. This can involve unwinding the coil, solutionizing the aluminum-based alloy sheet at a high temperature, quenching and recoiling. The above process, from start to finish, can take several weeks for preparing the coil for sale, resulting in large inventories of work in progress and final products, in addition to scrap losses at each stage of the batch process.

For example, an AA6XXX aluminum-based alloy sheet can be produced via a Direct Chill casting process which includes rolling of a thick AA6XXX (aluminum-based alloy ingot and thermo-mechanically processing the AA6XXX aluminum-based alloy strip obtained to produce a final AA6XXX aluminum-based alloy sheet having the required gauge. A series of heat-treatment steps are also required to yield a product in a temper (T4) that is formable and is an age-hardenable aluminum-based alloy sheet. Indeed, in order to produce the desirable aluminum-based alloy sheet, a homogenizing heat treatment step and a solutionizing heat treatment step are required.

In operation, and as shown in Prior Art FIG. 1, the aluminum-based alloy is cast via Direct Chill casting. Water cooling is used to obtain an aluminum-based alloy ingot that is solidified over its entire cross-section (i.e., its entire thickness). The obtained aluminum-based alloy ingot is typically 2 meters wide, 0.5 meter thick, and 5 meters long. During the course of the casting process, there is solute redistribution in the aluminum-based alloy ingot, which leads to both macrosegregation and microsegregation of the elements and intermetallics in the microstructure of the ingot. After the casting step, the rolling surface of the aluminum-based alloy ingot is scalped for subsequent rolling. However, before rolling can occur, the aluminum-based alloy ingot must be subjected to an homogenizing heat treatment step. The ingot is thus introduced into large furnaces to decrease or eliminate the microsegregation of its elements and to transform and/or change the morphology of some of its intermetallic phases. Typically, the homogenizing heat treatment step can be performed at a temperature of about 580° C., and involves ramp up time, hold time (typically 8 hours) and cool down time. Thus the homogenizing heat treatment step can basically take more than 12 hours. The heat-treated aluminum-based alloy ingot is then subsequently hot-rolled, cold-rolled and coiled to a gauge typically in the range of between about 0.5 mm and 2 mm.

In order to end up into useful parts, the aluminum-based alloy sheet must be subsequently subjected to a solutionizing heat treatment step to a T4 temper, where the aluminum-based alloy sheet can be heated quickly to a temperature where the main age-hardening/strengthening phase, Mg₂Si for example, can be put back into solid solution so it can be precipitated during the ageing process. This latest heat treatment step further strengthens the sheet.

During the Direct Chill casting process, Mg₂Si, for example, can be present in the AA6xxx aluminum-based alloy in two forms. One of these two forms comprises very finely dispersed Mg₂Si clusters. The dispersed Mg₂Si clusters are responsible for the increased strength during ageing and can be brought back into solution via the solutionizing heat treatment step. The other of these two forms comprises Mg₂Si globules formed during the DC casting operation. Such Mg₂Si globules or particles do not redissolve during the solutionizing heat treatment step and do not affect strengthening of the aluminum-based alloy sheet during the final ageing step of the process.

Because of the lengthy processing time in this flow path, numerous attempts have been made to shorten it by elimination of certain steps, while maintaining the desired properties in the finished aluminum-based alloy sheets. Moreover, because such heat treatment steps are energy-consuming and expensive, there is a need for an improved process for manufacturing an aluminum-based alloy sheet directly from the melt, which would be able to overcome or at least minimize some of the above-discussed concerns. The obtained aluminum-based alloy sheets need to have properties comparable to those of heat treated sheets, and the overall process needs to be performed in less process steps compared to conventional processes, and thus in a shorter period of time, and needs to involve less energy.

SUMMARY

It is an object of the present disclosure to provide a casting process for manufacturing an aluminum-based alloy sheet directly from a molten aluminum-based alloy that overcomes or mitigates one or more disadvantages of known manufacturing processes, or at least provides useful alternatives.

It is another object of the present disclosure to provide a casting process for manufacturing an aluminum-based alloy sheet directly from a molten aluminum-based alloy that includes a limited number of process steps, where the aluminum-based alloy sheet produced has at least some properties similar to or exceeding those of sheets provided with conventional processes.

In accordance with a non-limitative embodiment, there is provided a process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy. The process comprises: continuously casting and simultaneously cooling a substantially solid aluminum-based alloy strip thinner than about 10 mm using a belt caster, with a compression force on a solidifying aluminum-based alloy strip in a range of about 2 to about 3000 pounds per linear inch of alloy strip width.

In an embodiment, the continuously casting and simultaneous cooling is carried out at a cooling rate of between about 100 K/s and about 1500 K/s.

In accordance with a further non-limitative embodiment, there is provided a process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy. The process comprises, in a belt-cast sequence: continuously casting and simultaneously cooling a substantially solid aluminum-based alloy strip thinner than about 10 mm and cold-rolling the substantially solid aluminum-based alloy strip, without carrying out a quench nor a heat treatment step following the simultaneous casting and cooling and prior to the cold-rolling, to obtain the aluminum-based alloy sheet.

According to another general aspect, there is provided a process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy. The process comprises: continuously casting and simultaneously cooling an aluminum-based alloy strip thinner than about 10 mm using a belt caster, with a compression force on the aluminum-based alloy strip, during its solidification, in a range of about 2 to about 3000 pounds per linear inch of alloy strip width to obtain the aluminum-based alloy strip in a substantially solid state.

According to another general aspect, there is provided a process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy. The process comprises: in a continuous in-line sequence: continuously casting and simultaneously cooling an aluminum-based alloy strip thinner than about 10 mm, with a compression force on the aluminum-based alloy strip, during its solidification, in a range of about 2 to about 3000 pounds per linear inch of alloy strip width to obtain the aluminum-based alloy strip in a substantially solid state.

The process can further comprise pulse heating the aluminum-based alloy strip. The pulse heating can be performed at a temperature range of about 400° C. to about 570° C. and for a time period in a range of about 2 seconds to about 10 seconds.

In an embodiment, the pulse heating comprises pulse solutionizing, and the aluminum-based alloy is an age-hardenable aluminum-based alloy, such as a AA6XXX aluminum-based alloy and, more particularly, a AA6005 or AA6016 aluminum-based alloy.

In an embodiment, the pulse heating comprises pulse annealing, and the aluminum-based alloy is a strain hardenable aluminum-based alloy, such as a AA5XXX aluminum-based alloy and, more particularly, a AA5182 or AA3104 aluminum-based alloy.

According to a general aspect, there is provided a process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy. The process comprises: continuously casting and simultaneously cooling an aluminum-based alloy strip thinner than about 10 mm by feeding a belt caster with the molten aluminum-based alloy, with a compression force on the aluminum-based alloy strip, during its solidification, in a range of about 2 to about 3000 pounds per linear inch of alloy strip width to obtain the aluminum-based alloy strip in a substantially solid state.

According to another general aspect, there is provided a process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy. The process comprises: in a continuous in-line sequence: continuously casting and simultaneously cooling the molten aluminum-based alloy to obtain an aluminum-based alloy strip thinner than about 10 mm, while applying a compression force on the aluminum-based alloy strip, during its solidification, in a range of about 2 to about 3000 pounds per linear inch of alloy strip width to obtain the aluminum-based alloy strip in a substantially solid state.

The process can further comprise rolling the substantially solid aluminum-based alloy strip following the simultaneous casting and cooling to obtain the aluminum-based alloy sheet. For instance, the rolling can be cold-rolling, which can be performed at a temperature in a range of about room temperature to about 150° C. and, in some embodiments, at a temperature range of about room temperature to about 100° C.

In an embodiment, the compression force applied on the solidifying aluminum-based alloy strip ranges between about 10 to about 150 pounds per linear inch of alloy strip width. In another embodiment, the compression force applied on the solidifying aluminum-based alloy strip ranges between about 2 to about 100 pounds per linear inch of alloy strip width. In still another embodiment, the compression force applied on the solidifying aluminum-based alloy strip ranges between about 10 to about 100 pounds per linear inch of alloy strip width. In a further embodiment, the compression force applied on the solidifying aluminum-based alloy strip ranges between about 10 to about 60 pounds per linear inch of alloy strip width.

In an embodiment, the simultaneous casting and cooling is carried out with a belt caster.

In an embodiment, the process further comprises quenching the substantially solid aluminum-based alloy strip following the simultaneous casting and cooling and prior to the rolling. The process can be free of heat treatment step following the simultaneous casting and cooling and prior to the rolling.

In an embodiment, the process is free of quenching and heat treatment steps following the simultaneous casting and cooling and prior to the rolling, to obtain the aluminum-based alloy sheet.

In an embodiment, the process further comprises quenching the aluminum-based alloy sheet following the rolling. The process can further comprise artificially ageing the aluminum-based alloy sheet following the quench.

In an embodiment, the process further comprises artificially ageing the aluminum-based alloy sheet following the rolling.

In an embodiment, the simultaneously cooling is performed at a cooling rate of between about 100 K/s and about 1500 K/s.

In an embodiment, the process further comprises coiling the aluminum-based alloy strip following the simultaneously casting and cooling and uncoiling the coiled aluminum-based alloy strip before rolling the aluminum-based alloy strip.

In an embodiment, the aluminum-based alloy is an age-hardenable aluminum-based alloy.

In an embodiment, the aluminum-based alloy is a AA2XXX aluminum-based alloy, a AA4XXX aluminum-based alloy, a AA5XXX aluminum-based alloy, a AA6XXX aluminum-based alloy, or a AA7XXX aluminum-based alloy. For instance, it can be a AA6005 aluminum-based alloy, a AA6016 aluminum-based alloy, a AA5182 aluminum-based alloy, a AlMgSi-based alloy, and the like.

In an embodiment, the aluminum-based alloy is a AA5XXX aluminum-based alloy, the process further comprising heat treating the aluminum-based alloy sheet. For instance, the heat treatment can comprise annealing the aluminum-based alloy sheet.

In an embodiment, the substantially solid aluminum-based alloy strip has an as-cast gauge, and the aluminum-based alloy sheet has an as-rolled gauge being smaller than the as-cast gauge, the rolling is performed in continuous in-line sequence with the casting and simultaneously cooling and wherein the as-rolled gauge is obtained in a time interval of between about 1 second and about 15 seconds following the continuously casting and simultaneous cooling. The as-cast gauge can be between about 2 mm and about 5 mm. The as-rolled gauge can be between about 0.15 mm and about 4 mm.

In an embodiment, the obtained aluminum-based alloy sheet meets metallurgical requirements for use in transport applications. In an embodiment, the aluminum-based alloy is an AA6016 aluminum-based alloy, and wherein the obtained aluminum-based alloy sheet has a Yield Strength (YS) of above or equal to about 260 MPa and/or an Ultimate Tensile Strength (UTS) above or equal to about 270 MPa and/or an elongation of above or equal to about 6%.

In an embodiment, the obtained aluminum-based alloy sheet meets metallurgical requirements for use in beverage container applications. In an embodiment, the aluminum-based alloy is an AA5182 aluminum-based alloy, and wherein the obtained aluminum-based alloy sheet has an Ultimate Tensile Strength (UTS) above or equal to about 440 and/or an elongation above or equal to about 2%.

In an embodiment, the aluminum-based alloy is a AA6XXX aluminum-based alloy and the metallurgical requirements comprise properties of a T4. In an embodiment, the obtained aluminum-based alloy sheet has a Yield Strength (YS) above or equal to about 300 MPa and/or an Ultimate Tensile Strength (UTS) above or equal to about 310 and/or an elongation above or equal to about 4%.

In an embodiment, the aluminum-based alloy is a AA6XXX aluminum-based alloy and the metallurgical requirements comprise properties of an at least partially solutionized aluminum-based alloy sheet.

In an embodiment, the aluminum-based alloy is a AA6014 aluminum-based alloy, and wherein the obtained aluminum-based alloy sheet has at least one of a Yield Strength (YS) above or equal to about 290 MPa, an Ultimate Tensile Strength (UTS) above or equal to about 300, and an elongation above or equal to about 5%.

In an embodiment, at least about 80 wt % of the substantially solid aluminum-based alloy strip is in a solid state following the simultaneous casting and cooling.

In an embodiment, the compression force is between about 2 to about 150 pounds per linear inch of alloy strip width. In another embodiment, the compression force is between about 10 to about 100 pounds per linear inch of alloy strip width.

In an embodiment, the process further comprises pulse heating the aluminum-based alloy strip. Pulse heating can be performed at a temperature range of about 400° C. to about 570° C. Pulse heating can be performed for a time period in a range of about 2 seconds to about 10 seconds and, in some embodiments, for a time period of about 5 seconds.

In an embodiment, pulse heating comprises pulse solutionizing, and the aluminum-based alloy is an age-hardenable aluminum-based alloy, such as a AA6XXX aluminum-based alloy (e.g. AA6005 or AA6016).

In an embodiment, pulse heating comprises pulse annealing, and the aluminum-based alloy is a strain hardenable aluminum-based alloy, such as a AA5XXX X aluminum-based alloy (e.g. AA5182 or AA3104).

According to another general aspect, there is provided an aluminum-based alloy sheet manufactured using the process as described above, having a yield strength of between about 200 MPa and about 500 MPa and/or an ultimate tensile strength of between about 220 MPa and about 520 Mpa and/or an elongation of between about 1% and about 12%.

According to still another general aspect, there is provided an aluminum-based alloy sheet manufactured using the process as described above.

According to a further general aspect, there is provided the use of the aluminum-based alloy sheet as described above, for automobile panels, vehicle panels, reinforcements, beverage containers, or aerospace applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages and features will become more apparent upon reading the following non-restrictive description of embodiments thereof, given for the purpose of exemplification only, with reference to the accompanying drawings in which:

FIG. 1 shows a flowsheet of a conventional Direct Chill process for manufacturing a T4/T4P AA6XXX aluminum-based alloy sheet from a AA6XXX aluminum-based alloy (Prior Art).

FIG. 2 shows a flowsheet of a process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy in accordance with a non-limitative embodiment.

FIG. 3 shows a flowsheet of two processes for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy in accordance with two non-limitative embodiments.

FIG. 4 shows a flowsheet of a process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy in accordance with another non-limitative embodiment.

FIG. 5 shows an optical micrograph of a cross section of an AA6005 AlMgSi alloy strip, which is as-cast and etched with 0.5% HF at the indicated magnification level.

FIG. 6 shows an optical micrograph of a cross section of an AA6005 AlMgSi alloy strip having a thickness of 2 mm, which is as-cast and etched with a modified Barker's Reagent that includes boric acid, to show uniformity of cross-section grain size at the indicated magnification level.

FIG. 7 shows an optical micrograph showing microstructure at a surface of an AA6005 AlMgSi alloy strip having a thickness of 2 mm, which is as-cast and etched with 0.5% HF at the indicated magnification level.

FIG. 8 shows an optical micrograph showing microstructure at the centreline region of an AA6005 AlMgSi alloy strip having a thickness of 2 mm, which is as-cast and etched with 0.5% HF at the indicated magnification level.

FIG. 9 shows a plot of Ultimate Tensile Strength (UTS in MPa) vs. a ratio of Ultimate Tensile Strength to Yield Strength (UTS/YS, which is unitless or MPa/MPa) for 6 thin strip cast samples of AA6005 aluminum-based alloys.

FIG. 10 shows a plot of Yield Strength (YS) vs. a ratio of Ultimate Tensile Strength to Yield Strength (UTS/YS) for 7 thin strip cast samples of AA6005 aluminum-based alloys.

FIG. 11 shows a plot of Ultimate Tensile Strength (UTS in MPa) vs. a ratio of Ultimate Tensile Strength to Yield Strength (UTS/YS) for T4 conditions (T4 referring to temper, which means the samples have been solutionized and quenched) for 5 thin strip cast samples of AA6005 aluminum-based alloys.

FIG. 12 shows a plot of Ultimate Tensile Strength (UTS in MPa) vs. a ratio of Ultimate Tensile Strength to Yield Strength (UTS/YS) for samples that underwent ageing.

FIGS. 13A to 13D show plots of Ultimate tensile strength (UTS in MPa) and yield strength (YS in MPa), on the left Y axis, and Elongation (E in percentage), on the right Y axis, vs. elapsed time, in days, for as-cast AA6016 strips at the following casting and quenching conditions: 3 mm T4P (FIG. 13A), 3 mm water (FIG. 13B), 3 mm air (FIG. 13C), and 2 mm water (FIG. 13D).

FIGS. 14A to 14C are optical micrographs of cross sections of an AA6005 AlMgSi alloy strip having a thickness of 1 mm, which was cast by energy efficient belt casting (EEBC), and etched with a modified Barker's Reagent that includes boric acid, to show uniformity of cross-section grain size at the indicated magnification level. In FIG. 14A, the AA6005 AlMgSi alloy strip underwent pulse solutionizing at 500° C. for 5 seconds. In FIG. 14B, the AA6005 AlMgSi alloy strip underwent pulse solutionizing at 560° C. for 5 seconds. In FIG. 14C, the AA6005 AlMgSi alloy strip underwent conventional solutionizing at 560° C. for 60 seconds.

FIGS. 15A and 15B are optical micrographs of cross sections of an AA5182 AlMg alloy strip having a thickness of 1 mm, which was cast by EEBC, and etched with a modified Barker's Reagent that includes boric acid, to show uniformity of cross-section grain size at the indicated magnification level. In FIG. 15A, the AA5182 AlMg alloy strip underwent pulse annealing at 510° C. for 10 seconds. In FIG. 15B, the AA5182 AlMg alloy strip underwent batch annealing at 380° C. for 2 hours.

DETAILED DESCRIPTION OF EMBODIMENTS

Definitions

As used herein, the term “homogenizing heat treatment step” refers to a temperature ramp up time (typically with temperature ramp rate of 20 to 100° C. per hour. In some non-limitative implementations, the ramp up time can be around 12 hours), and hold time (typically between about 4 to about 12 hours and, in some implementations, around 8 hours) at an alloy temperature ranging between about 450° C. and about 600° C. (in some implementations around about 560° C.). In some non-limitative implementations, rolling can be performed directing after homogenization for solid diffusion. In other non-limitative implementations, the homogenization is followed by a cool down time, which can be, for instance and without being limitative around about 12 hours.

As used herein, the term “pulse annealing” of an aluminum alloy sheet refers to heating time (typically 3 to 10 seconds) at an alloy temperature ranging between about 450° C. and about 600° C. and, in some embodiments, between about 500° C. and about 560° C. (in some implementations around about 510° C.), and quickly cool down. In some implementations, the temperature cool down rate can range from about 20 to about 100° C. per hour. In some non-limitative implementations, the cooled down time can be around about 60 seconds. When referring to pulse annealing, the primary goal is to recrystallize the aluminum alloy sheet to achieve a good balance of strength and ductility, and not to solutionize.

When referring to “solutionizing” for a AA6XXX aluminum-based alloy, the primary goal is to solutionize Mg₂Si to enable later precipitation to affect age-hardening and thereby strength properties. However, it is appreciated that for other aluminum-based alloys, the phase to solutionize can differ. For instance, for AA7XXX aluminum-based alloy and AA2XXX aluminum-based alloy, MnZn and Al₂Cu phases are to be solutionized. As used herein, the term “pulse solutionizing” refers to heating time (typically about 3 to about 10 seconds) at an alloy temperature ranging between about 500° C. and about 570° C. and, in some implementations, around about 560° C., i.e. a temperature generally higher than those used for annealing, and is cold water quenched for immediate cool down. As used herein, the term “conventional solutionizing” refers to a heating time between about 30 seconds to about 90 seconds (typically around 60 seconds) at about 560° C., and is cold water quenched for immediate cool down.

As used herein, the term “batch annealing” refers to a temperature ramp up time for at least 6 hours and, sometimes, for more than 12 hours (typically around about 10 to about 12 hours), hold time for about 2 hours to about 8 hours (typically around 4 hours) at a temperature ranging between about 300° C. to about 450° C. (typical around 380° C.), and cool down time that typically totals between about 8 hours to about 20 hours (typically around 12 hours).

As used herein, the term “paint bake” refers to an artificial aging process having a heating time (typically about 30 minutes to about 60 minutes), at an alloy temperature ranging between about 170° C. and about 190° C. The goal of aging, or artificially aging, a AA6XXX aluminum-based alloy sheet is to precipitate Mg₂Si to affect strength properties. However, as mentioned above, it is appreciated that for other aluminum-based alloys, the phase to precipitate can differ. For instance, for AA7XXX aluminum-based alloy and AA2XXX aluminum-based alloy, MnZn and Al₂Cu phases are to be precipitated.

As used herein, the term “P” seen in terms “T6P” and “T4P”, refers to a pre-aging process having a heating time (typically for about 6 to 12 hours and, in some non-limitative implementations, around 8 hours), at an alloy temperature of about 75° C. to about 85° C. The goal of pre-aging an aluminum alloy sheet is to stabilize the microstructure to prevent brittleness caused by natural aging.

As used herein, the term “T4” seen in the term “T4P” refers to a solutionized sheet product.

As used herein, the term “T6” seen in the term “T6P” refers to an artificially aged sheet product.

EMBODIMENTS

A continuous belt-casting process for manufacturing an aluminum-based alloy sheet directly from a molten aluminum-based alloy is described. In a continuous sequence, and directly from the molten aluminum-based alloy, a substantially solid and substantially thin aluminum-based alloy strip is continuously cast and simultaneously cooled. The cast and cooled aluminum-based alloy strip has a thickness smaller than about 10 mm. It also has a microstructure mostly characterized by equi-axed grains. During the simultaneous casting and cooling operation, a compression force (or rolling force), which is in a range of about 2 to about 3000 pounds per linear inch of strip width, can be applied to a solidifying solid aluminum-based alloy strip following casting of the melt and while the alloy strip is being cooled and thereby during its solidification. The substantially solid aluminum-based alloy strip can then rapidly be rolled and, more particularly, cold-rolled, so as to obtain the aluminum-based alloy sheet. Indeed, in one implementation of the process, no additional or intermediate heat treatment step needs to be carried out between the simultaneous casting and cooling step, and the following cold-rolling step. This continuous casting process is referred to herein as “energy efficient belt casting (EEBC)”.

In one scenario, the cooling can be performed at a cooling rate of between about 100 K/s and about 1500 K/s. In one implementation, the rolling, following the simultaneous casting and cooling, is cold-rolling which can be performed at an alloy temperature (or strip temperature) between room temperature and 250° C. In one embodiment, cold rolling is performed at a strip temperature lower than about 150° C. and, in some implementations, at a temperature lower than about 80° C. The rolling, which can be cold-rolling, can thus be conducted substantially rapidly, in a continuous and in-line process, after the simultaneous casting and cooling operation. In an alternative embodiment, the aluminum-based alloy strip can be coiled following the casting/cooling step and, eventually, uncoiled to be rolled. Optionally, the produced aluminum-based alloy sheet can subsequently be heat treated, annealed for example, to obtain a final sheet that meets the requirements of a conventional and at least partially solutionized aluminum-based alloy, such as and without being limitative the T4 or the T4P requirements, without compulsorily carrying out a heat treatment between the casting/cooling step and the rolling step. In some implementations, no solutionizing heat treatment is carried out on the rolled aluminum-based alloy sheet.

As mentioned above, a compression force is applied on the solid aluminum-based alloy strip while it solidifies as it is cooled during the casting/cooling step. Compression force is also referred to as “separating force” or “rolling force”, i.e. the load between the top and bottom belts as the wedge of material solidifies. The compression force is applied on the alloy strip from the moment it includes a solid shell containing molten alloy until the strip exits the caster in a substantially solid state. During the EEBC casting/cooling process, the thickness of the solid shell increases as the alloy constituting the strip solidifies. In some embodiments, the alloy strip exiting the caster is at least 80 wt % solid and, in some embodiments, at least 90 wt %.

As mentioned above, the compression force results from the load between the top and bottom belts as the wedge of material solidifies. It can be measured using standard load cells (for instance and without being limitative four load cells), located between the top & bottom carriages, i.e. the structure including the pulleys around which the casting belts revolve. The compression force can be monitored and can be controlled by adjusting the speed of the belt caster. For instance, if increasing compression forces (or loads) are monitored, the belt caster speed can be increased to lower the compression force applied on the solid aluminum-based alloy strip while it solidifies. The measured compression force can be an indirect measurement of the aluminum state (how much solid the aluminum is) in the caster mold. More particularly, higher compression forces can indicate a more solid aluminum in the caster mold.

As described in more details below, even though the process described herein includes a limited number of process steps, more particularly between the simultaneous casting and cooling step and the rolling step, the aluminum-based alloy sheet produced has at least some mechanical properties similar to, or exceeding, those of aluminum-based alloy sheets obtained with conventional processes that include additional heat treatment steps, such as an homogenizing heat treatment step, between the casting step and the cold-rolling step. Indeed, an aluminum-based alloy sheet which meets metallurgical requirements for use in a variety of applications, including applications in the transport industry, the beverage container industry, etc. can be manufactured. The aluminum-based alloy sheet having the desired mechanical properties can thus be manufactured directly from the melt, and in a more efficient manner (without additional heat treatment steps).

The EEBC process described below thus obviates the need for many of the process steps that are absolutely needed in a conventional process, with a reduction in at least one of processing complexity, material handling and cost. As mentioned above, this can be achieved by simultaneously casting and cooling the molten aluminum-based alloy to produce the substantially solid and substantially thin aluminum-based alloy strip, and by directly and sufficiently quickly or subsequently rolling the substantially solid and substantially thin aluminum-based alloy strip to produce the aluminum-based alloy sheet so the strengthening phase can be effectively retained in solution. It is further noted that the present process allows the as-cast substantially solid aluminum-based alloy strip to sustain a relatively important amount of cold reduction (e.g., 90% or less and, in some implementations, 75% or less) to yield a final aluminum-based alloy sheet of the required thickness (e.g., 0.2 to 4 mm and, in some implementations, 0.5 to 4 mm), as described below.

The EEBC process described herein can thus allow, where the aluminum-based alloy is a AA6XXX aluminum-based alloy for example, for the manufacturing of a AA6XXX aluminum-based alloy sheet that has at least some of the mechanical properties of an at least partially solutionized AA6XXX aluminum-based alloy sheet (i.e., of an AA6016-T4 sheet), even though no solutionizing heat treating step has been performed on the substantially solid aluminum-based alloy strip after it has been cast, and before it is cold-rolled. To achieve this temper using a conventional process, the aluminum-based alloy strip is homogenization heat-treated or solution heat-treated following the casting operation and the cold-rolling operation, followed by naturally ageing. According to the process described herein, the substantially solid AA6XXX aluminum-based alloy strip can instead be aged, directly from the melt, and without the need of an additional or intermediate heat treatment step, such as an additional solutionizing heat treatment step following the rolling step, which can be a cold-rolling step.

In the present description, the aluminum-based alloy that is cast can be either strain-hardenable or age-hardenable and can include, for example, a AA2XXX aluminum-based alloy, a AA4XXX aluminum-based alloy, a AA5XXX aluminum-based alloy, a AA6XXX aluminum-based alloy or a AA7XXX aluminum-based alloy. For instance, and without being limitative, the AA2XXX aluminum-based alloy can include a AA2008 aluminum-based alloy, the AA5XXX aluminum-based alloy can include a AA5182 aluminum-based alloy or a AA5754 aluminum-based alloy, the AA6XXX aluminum-based alloy can include a AA6005 aluminum-based alloy, a AA6016 aluminum-based alloy, a AA6022 or a AA6011 aluminum-based alloy, and the AA7XXX aluminum-based alloy can include a AA7075 aluminum-based alloy.

The EEBC process is applicable also to new and non-conventional alloys as it has a wide operating window both with respect to belt casting and subsequent rolling, which can be performed in an in-line processing. In one implementation of the process, the aluminum-based alloy to be cast can be an aluminum-based Si-containing alloy and, more particularly, an aluminum-based MgSi-containing alloy (i.e., a AlMgSi-based alloy). It is noted that other age-hardenable aluminum-based alloy can be used to produce the aluminum-based alloy sheet. In other words, the process can involve any aluminum-based alloy that requires age hardening, allowing the resulting sheet product to meet the metallurgical requirements for use in the transport industry (e.g., automotive sheets, aerospace sheets, etc.), the beverage container industry, etc., or to meet the metallurgical requirements for manufacturing any other product that involves age-hardenable aluminum-based alloy sheets.

As used herein, the term “solution heat treatment” or “solutionizing heat treatment” refers to a metallurgical process in which the aluminum-based alloy is held at a high temperature so as to cause the second phase particles of the alloying elements to dissolve into solid solution. Temperatures used in solution heat treatment are generally higher than those used in annealing, and range up to about 570° C. and in some implementations between about 500° C. and about 570° C. This condition is then maintained by quenching of the metal for the purpose of strengthening the final product by controlled precipitation (ageing).

As also used herein, the term “substantially solid aluminum-based strip” refers to the aluminum-based alloy in the substantially thin strip form. The substantially solid aluminum-based strip of the present disclosure can be produced by any number of apparatus for continuously casting a substantially solid and substantially thin aluminum-based alloy strip from a molten aluminum-based alloy, that are well known to those skilled in the art. One apparatus for forming the substantially solid and substantially thin aluminum-based alloy strip is described in U.S. Patent Publication No. 2018/0290204 assigned to Hazelett Strip Casting Corp, which is incorporated by reference herein. For example, the continuously-cast aluminum-based alloy strip can have a thickness smaller than 10 mm and, in some embodiments, the continuously-cast aluminum-based alloy strip can range from about 2 to about 5 mm in thickness. It is also noted that at least 80 wt % of the substantially solid aluminum-based alloy strip can be in a solid state just downstream of the simultaneous casting and cooling step. In some implementations, at least 95 wt % of the aluminum-based alloy strip is in the solid state just downstream of the simultaneous casting and cooling step. The substantially solid aluminum-based strip can be produced using a belt caster (such as a twin-belt caster) or alternatively, a roll caster. In one scenario, the caster is operated with a compression force in a range of about 2 to about 3000 pounds per linear inch of strip width applied to a continuously cast alloy strip while it solidifies so that the produced strip can have a microstructure comprised of equi-axed grains, as described below. In some implementations, the compression force is higher than about 2 pounds per linear inch of strip width and lower than about 1000 pounds per linear inch of strip width. In some embodiments, it is lower than about 500 pounds per linear inch of strip width, in some embodiments, lower than about 150 pounds per linear inch of strip width and, in still other embodiments, less than about 100 pounds per linear inch of strip width. In other embodiments, the compression force is between about 2 to about 100 pounds per linear inch of strip width. In still other embodiments, the compression force is between about 10 to about 100 pounds per linear inch of strip width and, in further embodiments, the compression force is between about 10 to about 60 pounds per linear inch of strip width.

When the simultaneous casting and cooling process is performed with a belt caster, molten metal is injected between two counter-rotating belts, i.e. between an upper belt and a lower belt. More particularly, the molten metal is injected thru a rigid refractory (nonreactive to the melt) injector (also referred to as a ‘nosepiece’ or ‘snout’) into the parallel and straight section between the belts as a means of delivering liquid metal to the externally cooled belt surfaces. The parallel and straight section between the two belts defines a mold for the metal solidification. The belts are wrapped around two pulleys and supported by back up rolls in the straight section on the back side of the belts, as illustrated in FIG. 1 of US patent application no. 2018/0290204, which is incorporated herein by reference.

In conventional belt-casting, the molten metal first contacts the belt past a pulley tangent point where the belt is not yet supported by back up rolls. The unsupported belt is thus subject to thermal shock from molten metal and a belt take-off. Belt take-off refers to the natural tendency of a tensioned belt to come away from its radiused or planar guide surface when subject to a bending moment. It has been observed that such conditions make the belt very unstable where the initial solidification occurs, as illustrated in FIG. 2 of US patent application no. 2018/0290204. Thus, the compression force applied by the belts on the molten and solidifying metal is minimal since the molten metal solidifies at the same thickness as the mold opening defined by the gap between two parallel belts.

It has been observed that, molten metal can be fed on the curved region of the belt, upstream of the beginning of the parallel and straight section, as illustrated in FIG. 3 of US patent application no. 2018/0290204. As shown, the belts are supported by curved mold support sections where molten metal first meets the belt. As detailed in the description of US patent application no. 2018/0290204, the large radius portion of the mold defined by the belt supports eliminates or significantly reduces the possibility of belt take-off at the tangent of the comparatively small, fixed radius nip roll where the belt transitions from a curved to planar path. As a result, the mold entry region becomes very stable, allowing casting thinner strips.

Since the molten metal first contacts the belt in the curved region where the belts are converging, a strip thickness can be larger than a spacing height in the parallel and straight section (also referred to as mold opening). Once entering the parallel and straight section, the belts exert a compression force on the alloy strip 18 while it solidifies. It has been observed that even a small compression force (about 2 pounds per linear inch of strip) would be conducive to the extended contact between belts and metal strip and benefit solidification.

Depending on the metal feeding point (feeding nozzle setback) and speed of casting, the compression force can vary significantly. For example, if the molten metal is fed very close to the beginning of the parallel section in the mold and the belts travel at a high speed, the metal strip could be not fully solidified when entering the nip (the smallest clearance in the mold), therefore the rolling force could be very small.

The term “homogenization” or “homogenization heat treatment step” is also used herein. Homogenization of an alloy is done to provide sufficient time at a specific temperature for the microsegregation, which occurs during the Direct Chill casting step, to be “leveled” by diffusion of elements within the microstructure. That is, during the solidification process alloys that contain appreciable solute microsegregation (termed ‘coring’) occurs across the dendrite/cells. In conventional processing, unless homogenized, such materials cannot be successfully rolled without fracturing in the rolling mill due to the extent of coring. This behaviour is known to happen in alloy families such as AA2XXX, AA4XXX , AA5XXX , AA6XXX and AA7XXX. By providing sufficient time at a specific temperature for the nonequilibrium solute levels in the cast ingot to level, the material can subsequently be rolled without cracking. For aluminum alloys in conventional processing, homogenization is typically performed in the range of about 450° C. to about 600° C., a range of temperature over which other metallurgical processes may also simultaneously occur, via recrystallization, solutionizing, intermetallic phase transformation, etc.

As also used herein, the term “anneal” refers to a heating process that causes recrystallization of the metal to occur, producing uniform formability and assisting in earing control. Typical temperatures used in annealing aluminum alloys range from about 315 to 490° C. for longer than a few minutes. The annealing heat treatment step is used to reduce or remove residual stresses in the alloy, by reducing its stored energy, without significantly lowering its tensile strength. In aluminum metallurgy, the annealing heat treatment can be comprised of three steps, namely, recovery, recrystallization and grain growth. Reducing the stored energy has the effect of eliminating atomic level defects, primarily dislocations, due to atomic level lattice mismatch, in the alloy. During the early stages of annealing, the alloy experiences recovery, at temperatures up to about 300° C., and, thereafter, recrystallization. Depending upon the alloy composition, it is possible to transform insoluble intermetallic species and to age the alloy during annealing.

Recovery is the metallurgical process of reducing the stored energy by the elimination or reduction of defects in the crystal lattice and precedes recrystallization. Often, there is only a very slight decrease in the strength of the material from a recovery heat treatment. Recovery heat treatments are performed below about 300° C.

On the other hand, recrystallization is a metallurgical process wherein a worked material, when heated above its recovery temperature, forms domains (i.e., grains) of atoms that have, within them, a similar atomic lattice orientation. The formation of grains leads to a large decrease in tensile strength of the material. For aluminum alloys, recrystallization commences around about 300° C. for most alloys.

Finally, grain growth occurs subsequent to the recrystallization process at temperatures above about 300° C. and involves the growth of larger, more energetically favoured crystallographic orientations, at the expense of smaller higher energy grains. The tensile strength of aluminum decreases with increased grain size.

It is also noted that age hardening is a metallurgical process wherein an alloy with a supersaturated solid solution can be suitably heat treated to form stable precipitates in a solid that are of the correct size and distribution to impede and/or pin dislocation movement, which is required for plastic deformation. Alloy systems such as AA2XXX, AA6XXX and AA7XXX systems rely on age hardening for a significant proportion of their high strength performance. Age hardening is a particularly potent means of strengthening aluminum alloys.

It is further noted that aluminum has limited solid solubility with most other alloying elements. Notable exceptions are with Mg (AA5XXX) and Li (AA8XXX) alloys. Solid solution strengthening relies on atoms with sizes similar to that of aluminum being substantially positioned in the crystal lattice. The presence of slightly “off-size” atoms impedes the movement of dislocations during deformation and strengthens the material. Solid solution strengthening typically only provides a modest increase to the yield/ultimate tensile strength of aluminum alloys. However, it has a large effect upon the work hardening rate. Indeed, when aluminum is plastically deformed, it generates dislocations that increases aluminum resistance to further deformation. The presence of more substitutional atoms in the crystal lattice (e.g., Mg and Li) increases the rate of dislocation generation (i.e., the tensile strength) of the alloy at a higher rate than for solute that is not substitutional in the crystal lattice. The rate of strength increases with increasing deformation (strain) is referred to as its work hardening rate.

Typically, the grain structure obtained following the casting/cooling step is a grain structure consistent with two opposing solidification fronts. In some implementations, the grain structure comprises equi-axed grains, i.e. grains of an alloy that show no directionality and tend to be similarly-sized in all directions, as shown in FIG. 6.

Referring now to the drawings and more particularly to the non-limitative embodiment of FIG. 2, there is shown a process 10 for manufacturing an aluminum-based alloy sheet 12 directly from a molten aluminum-based alloy 14 (i.e., directly from the melt 16). Sequentially, and directly from the molten aluminum-based alloy 14, a substantially solid and substantially thin aluminum-based alloy strip 18 is continuously cast and simultaneously cooled, in a continuous casting and cooling system 20. In one implementation, the substantially solid aluminum-based alloy strip 18 can simultaneously be cast and cooled in a belt caster, in the belt caster as well described in U.S. Patent Publication No. 2018/0290204 assigned to Hazelett Strip Casting Corp, for example. However, in another implementation, the substantially solid aluminum-based alloy strip 18 can simultaneously be cast and cooled in a roll caster. It is noted that any casting device producing a substantially solid and substantially thin aluminum-based alloy strip 18 while applying a compression force thereto during casting in a range of about 2 to about 3000 pounds per linear inch of strip width can be used, as mentioned above. As mentioned above, the compression force is applied on the solidifying aluminum-based alloy strip 18, i.e. as the melt solidifies inside a solid alloy shell, by the two belts (upper and lower belts) which are located on each side of the aluminum-based alloy strip 18 during the simultaneous casting and cooling step. In some embodiments, the compression force applied to the melt and on the resulting strip during the casting/cooling step is higher than about 2 pounds per linear inch of strip width and lower than about 1000 pounds per linear inch of strip width and lower than about 150 pounds per linear inch of strip width. In other embodiments, the compression force is between about 2 to about 100 pounds per linear inch of strip width. In still other embodiments, the compression force is between about 10 to about 100 pounds per linear inch of strip width and, in further embodiments, the compression force is between about 10 to about 60 pounds per linear inch of strip width. The thin aluminum-based alloy strip 18 has a grain structure consistent with two opposing solidification fronts and which can comprise equi-axed grains. The thin aluminum-based alloy strip 18 has a thickness smaller than about 10 mm, in some embodiments, thinner than about 6 mm, and still other embodiments, thinner than about 4 mm. In some embodiments, the aluminum-based alloy strip 18 is thicker than about 2 mm.

The casting apparatus is operated at a casting speed that can be varied in accordance with the thickness of the cast strip. In some implementations, a product of the casting speed (in meter per minute) and the thickness of the strip 18 (in mm) ranges between 120 and 200, depending on a length of the cooling zone in the casting apparatus. For instance, for casting a 4 mm thick aluminium-based strip, the casting speed can range between 30 m/min and 50 m/min. For casting a 2 mm thick aluminium-based strip, the casting speed can range between 60 m/min and 100 m/min.

As mentioned above, the aluminum-based alloy strip 18 is simultaneously cooled as it is cast. Cooling rate was determined using dendrite arm spacing as described in Miki et al. (Japanese Institute of Light Metals, vol. 25, issue 1, p. 1-9 (1975)) and in Spear and Gardner (Trans. AFS, vol 71, p. 209 (1963)). In one scenario, the cooling can be performed at a cooling rate of between about 100 K/s and about 1500 K/s and, in another scenario, the cooling can be performed at a cooling rate of between about 500 K/s and about 1200 K/s. Once again, the cooling rate can vary in accordance with the thickness of the cast strip. Typically, the thicker the cast strip 18 is then the slower the cooling rate. In some implementations, for a 10 mm thick cast strip, the cooling rate is between about 100 K/s to about 400 K/s while, for a 2 mm thick cast strip, the cooling rate is between about 1200 K/s to about 1500 K/s

In some implementations, the substantially solid aluminum-based alloy strip 18 can then be rolled, substantially rapidly, in a continuous in-line process with the simultaneous casting/cooling step, and, more particularly, in some implementations, cold-rolled substantially rapidly, by passing through a rolling system 22 including one or more roll(s), so as to obtain the aluminum-based alloy sheet 12.

In other implementations, the substantially solid aluminum-based alloy strip 18 can be stored for a period of time before being rolled. For instance, it can be coiled into a roll and, then unrolled, before being rolled. For instance, the storage period between the simultaneous casting/cooling step and the following rolling step can be between 1 day and up to about 60 days. In one implementation, it can be between about 5 days and about 60 days.

As mentioned above, the rolling stage can be cold rolling wherein the cast strip 18 has a temperature below 250° C. It can also be warm rolling, wherein the cast strip has a temperature between about 150° C. and about 250° C., or even hot rolling (temperature above about 250° C.).

In some implementations wherein the substantially solid aluminum-based alloy strip 18 is cold-rolled, substantially rapidly, in a continuous in-line process with the simultaneous casting/cooling step, the temperature of the substantially solid aluminum-based alloy strip 18 is maintained below 250° C. following the simultaneous casting/cooling step and before the cold-rolling step.

For example, the substantially solid aluminum-based alloy strip 18 can simultaneously be cast and cooled so that it has an as-cast gauge of below about 10 mm and, in some implementations, between about 2 mm and about 5 mm. On the other hand, the substantially solid aluminum-based alloy strip 18 can be rolled, for instance and without being limitative, cold-rolled so that the aluminum-based alloy sheet 12 obtained has an as-rolled gauge of between about 0.5 mm and about 4 mm. In a system wherein the process is carried-out continuously and in-line, benefiting from the substantially high cooling rate provided by the casting and cooling system 20, the as-rolled gauge of the aluminum-based alloy sheet 12 can be obtained in a substantially short time interval. For example, the desired as-rolled gauge of the aluminum-based alloy sheet 12 can be obtained after less than about 25 seconds, and in some embodiments, only between about 1 second and about 25 seconds.

For example, the substantially solid aluminum-based alloy strip 18 can be rolled at a temperature lower than its solutionizing temperature, for example, at a strip temperature lower than about 300° C. (i.e., temperature of the strip just before entering the rolling system 22). As mentioned above, in one implementation of the process, no additional or intermediate heat treatment step, no additional or intermediate homogenization heat treatment step for example, needs to be carried out between the casting and cooling system 20 and the rolling system 22. In some implementations of the process described herein, the substantially solid aluminum-based alloy strip 18 that has been cast is thus directly and rapidly rolled and, more particularly, directly and rapidly cold rolled, without re-heating the substantially solid aluminum-based alloy strip 18 between the casting and cooling system 20 and the rolling system 22. Therefore, the substantially solid aluminum-based alloy strip 18 can enter the rolling system 22 at a strip temperature lower than about 300° C. and, in other implementations at a strip temperature lower than about 150° C.

In other implementations of the process described herein, as shown for instance in FIG. 3, the substantially solid aluminum-based alloy strip 18 that has been cast is stored before being rolled. For instance, it can be coiled for storage purposes. The substantially solid aluminum-based alloy strip 18 can optionally be quenched 28 before it is rapidly coiled. Quenching can be performed to further diminish the rate of any incipient ageing that may occur prior to the rolled sheet reaching its storage/shipping temperature. Then, following storage and shipment, if any, it can be uncoiled, if required, and subsequently, rolled, for instance cold-rolled. If required, it can be re-heated before being rolled in the rolling system 22. In these implementations, the substantially solid aluminum-based alloy strip 18 is heated before the rolling stage to enter the rolling system 22 at a strip temperature lower than about 250° C. and, in other implementations at a strip temperature lower than about 150° C.

Referring now more particularly to the non-limitative embodiments of FIGS. 3 and 4, it is noted that the produced aluminum-based alloy sheet 12, after it has been rolled, can further be heat treated. This subsequent heat treatment can be performed in a continuous in-line sequence with the rolling stage. For example, the produced aluminum-based alloy sheet 12 can be subjected to a solution heat treatment stage 24 and solutionized (see left side of FIG. 3), or alternatively, subjected to an annealing device 26 to be annealed. In other words, additional heat treatment stages can be involved in the process 10, after the cold-rolling of the substantially solid aluminum-based alloy strip 18. These additional heat treatments are thus performed on the obtained aluminum-based sheet 12. For example, large furnaces or ovens can be used for the solutionizing heat treatment step and/or the annealing heat treatment step. After the solutionizing heat treatment step or the annealing heat treatment step, the aluminum-based alloy sheet 12 can optionally be quenched 28 (e.g., air or water quenched), coiled 30 and pre-aged 32. The ageing/pre-ageing step can be an artificial ageing step. In some implementations, an artificial ageing step can be performed without any solutionizing heat treatment step between the rolling step and the artificial ageing step. In other implementations, an anneal and quench was performed following the rolling step to allow for formability. Following forming, an artificial ageing step was performed to strengthen the newly formed part. For instance, for artificial ageing, the aluminium-based alloy sheet 12 can be maintained in an environment between about 150° C. and about 250° C. for about 15 minutes to about 8 hours and, in some implementations, for about 5 hours to about 8 hours. Artificial ageing can also occur during paint baking. It can also include a pre-ageing step wherein the aluminium-based alloy sheet 12 can be maintained in an environment between about 50° C. and about 100° C. for about 5 hours to about 8 hours. Still referring to the non-limitative embodiment of FIG. 2, the substantially solid aluminum-based alloy strip 18 can optionally be quenched before it is rapidly coiled and, subsequently, rolled. Quenching can be performed to further diminish the rate of any incipient ageing that may occur prior to the rolled sheet reaching its shipping temperature.

In operation, the substantially solid aluminum-based alloy strip 18 can be directly rolled and, more particularly, cold-rolled, to its as-rolled gauge and then, be artificially aged. Indeed, by casting an aluminum-based Mg₂Si-containing alloy, for example, at a sufficiently high cooling rate, it is possible to put more of the Mg₂Si into solution and suppress the formation of Mg₂Si globules and/or eliminate its interdendritic form entirely. The aluminum-based alloy sheet 12 obtained can thus have a similar strength (i.e., at least one of Yield Strength (YS), Ultimate Tensile Strength (UTS) and Elongation) to that of an aluminum-based alloy sheet resulting from a conventional Direct Chill process having the same chemical composition. However, since the aluminum-based alloy sheet 12 resulting from the present process 10 has more cold work therein, the resulting sheet 12 can also have a lower elongation to failure than that of an aluminum-based alloy sheet resulting from the conventional Direct Chill process.

In an embodiment, the EEBC continuous belt-casting process described above further comprises a pulse heating step, which will be referred to hereinafter as “EEBC+Pulse”. The pulse alloy heating is carried out following the simultaneous casting and cooling step and the subsequent cold-rolling step.

Due to its effect on the aluminum alloy, pulse heating may be referred to herein as pulse solutionizing when describing pulse heating of age-hardenable aluminum alloys (i.e., 6xxx series). Similarly, pulse heating may be referred to herein as pulse annealing when describing pulse heating of strain hardenable aluminum alloys (i.e., 5xxx series).

As used herein, the term “pulse solutionizing” refers to an increase of the alloy temperature, typically, at an alloy temperature ranging between about 500° C. and about 570° C. and, in some implementations, around about 560° C., for a relative short heating time (typically about 3 to about 10 seconds), followed by a quench. Furthermore, the rapid temperature increase is quickly followed by a quench for immediate cool down. In some implementations, the quench is a cold-water quench.

When referring to pulse annealing, the primary goal is to recrystallize the aluminum alloy sheet to achieve a good balance of strength and ductility, and not to solutionize. As used herein, the term “pulse annealing” of an aluminum alloy sheet refers to an increase of the alloy temperature, typically, at an alloy temperature ranging between about 450° C. and about 600° C. and, in some embodiments, between about 500° C. and about 560° C. (in some implementations around about 510° C.), for a relative short heating time (typically 3 to 10 seconds) followed by a cool down immediately after the temperature increase. In some implementations, the temperature cool down rate can range from about 20 to about 100° C. per hour. In some non-limitative implementations, the cooled down duration can be around about 60 seconds.

In an embodiment, the pulse heating step carried out in combination with the above-described EEBC removes the need for conventional solutionizing. More particularly and surprisingly, the EEBC+Pulse process can remove the need for conventional solutionizing of age-hardenable (i.e., 6xxx series) aluminum alloys. Additionally, it can reduce the need for annealing of strain hardenable (i.e., 5xxx series) aluminum alloys. In this way, it can potentially reduce an aluminum casting facility footprint and, more particularly, an aluminium sheet production facility footprint (i.e. allows for a reduced length of processing line).

In an embodiment, to quickly heat the aluminum-based alloy sheet 12 to perform pulse solutionizing or pulse annealing thereon, infrared heater(s) can be used. In an embodiment, during the quick temperature increase substantially the entire aluminum-based alloy sheet 12 will reach the target temperature, even in a center thereof.

In addition, the aluminum alloy sheets that are obtain via the EEBC+Pulse process can exhibit equivalent or improved strength and ductility when compared to aluminum alloy sheets that were processed using conventional solutionizing, as will be described in more details below in reference to the results shown in Table 4.

Thus, the EEBC+Pulse processing can enable casting of solutionized aluminum alloy sheet with less than 10 seconds of heating, typically only about 5 seconds of heating. When compared to about 60 seconds of heating that is needed in a conventional solutionizing process, the EEBC+Pulse can further allow for a reduction in energy consumption, and ultimately, operation costs. In a non-limitative embodiment, it can be estimated that the EEBC+Pulse process can consume about 75% less energy and can create a significant amount (possibly as high as 90%) less waste compared to the conventional ingot processing method. Additionally, in some implementations, the footprint of the EEBC+Pulse line can be smaller than the one of conventional processing lines for producing aluminum sheets (e.g., aluminum automotive body sheets). In a non-limitative embodiment, an EEBC+Pulse processing line can convert liquid aluminum to a 10 ton coil of 2 mm sheet in about 70 meters and about 20 minutes. To produce the same quantity of aluminum sheet, the footprint of a conventional solutionizing line can require an order of magnitude larger footprint in terms of the square area coverage. Furthermore, the time required to convert liquid aluminum to 2 mm sheet via the conventional DC ingot method can typically take 20 or more days. In comparison with a conventional processing line, the EEBC+Pulse line can have low capital and operating costs, with a small plant footprint and can provide at least equivalent aluminum sheets using short processing times to final product. Accordingly, the EEBC+Pulse process can provide at least one of an economic advantage and an environmental advantage over existing technologies.

Therefore, the present process allows to, directly from a molten aluminum-based alloy 14, simultaneously cast and cool a substantially solid aluminum-based alloy strip 18 of a substantially thin as-cast gauge (thinner than about 10 mm), using for example, a belt caster. Since the substantially solid aluminum-based alloy strip 18 can be cooled at a sufficiently high cooling rate, the produced aluminum-based strip 18 can be directly processed to an aluminum-based alloy sheet having at least some mechanical properties similar to a solutionized T4 (age-hardenable) temper, without the need for an intermediate homogenization heat treating step between the casting and cooling system 20 and the rolling system 22 and, more particularly, without the need of an homogenization heat treatment step between the simultaneous casting and cooling step and the cold-rolling step. Furthermore, the process described herein can further include heat treating the rolled aluminum-based alloy sheet 12 (i.e., after the cold-rolling step) to reduce the amount of hardening via working of the alloy that may be due to an inline pinch roll (for gauge and profile control), and subsequent rolling steps. A separate, or alternatively, in-line, recovery step can thus be performed. The aluminum-based alloy sheet 12 obtained is fairly uniform in cross-section, and exhibits slight coarsening towards the cast centreline.

The process described herein, that allows cooling from the melt to a rollable thin strip, has many benefits over the prior art processes. First, by simultaneously casting and cooling the substantially solid aluminum-based alloy at a substantially high cooling rate (i.e., at a cooling rate of about 1,500 K/s to about 100 K/s vs. 10 K/s for conventional processes), more alloy elements are put into solid solution. Increased amounts of certain phases in solid solution (e.g., Mg₂Si in AA6XXX series alloys) makes the alloy more effectively age-hardenable. Second, by being able to put sufficient amounts of the age-hardening (i.e., strengthening) phase into the as-cast substantially solid aluminum-based alloy strip, the strip can be successfully aged, without any additional or intermediate heat treatment stages that are usually necessary in conventional sheet processing routes.

As mentioned above, the resulting aluminum-based alloy sheet can thus end up with characteristics that meet at least partially the metallurgical requirements for use in transport applications, for example. Indeed, a common alloy used in the manufacture of transportation aluminum-based products is the AA6016 aluminum-based alloy. Typical mechanical properties for a conventionally produced, solution heat treated and aged AA6016 in the T6 temper can be as follow: Yield Strength (YS)≥210 MPa, Ultimate Tensile Strength (UTS)≥240 MPa, Elongation≥12%. On the other hand, mechanical properties for a produced AA6016 sheet resulting from the present process (simultaneous casting and cooling, followed by cold-rolling and ageing) can range as follow: YS: between about 250 and about 260 MPa; UTS: between about 260 and about 280 MPa; and between about elongation is between about 7% and about 8%.

Moreover, the resulting aluminum-based alloy sheet can end up with characteristics that meet at least partially metallurgical requirements for use in beverage container applications, for example. Indeed, a common alloy used in the manufacture of beverage container aluminum-based products is the AA5182 aluminum-based alloy, which can form, for example, the top of a can. It is critical that the supplied aluminum-based sheets have suitable mechanical properties in the fully hard and stoved condition. Stoving is the process where, after the container has been filled, it is heated for a period of time above the boiling point of water to pasteurize the liquid being contained therein. Typical mechanical properties for a conventionally stoved AA5182 sheet can be as follows: Yield Strength (UTS): 340-395 MPa, Elongation≥5%. On the other hand, mechanical properties for a produced AA5182 sheet resulting from the present process (simultaneous casting and cooling, and cold-rolling from an as-cast gauge of 2 mm to an as-rolled gauge of 0.208 mm) can range as follows: YS: between about 420 and about 450 MPa, UTS: between about 440 and about 470 MPa, and Elongation: between about 2% and about 5%. Mechanical properties following a subsequent stoving can range as follow: YS: between about 350 and about 370 MPa and elongation is between about 7 and about 10%.

It is noted that, in general, the aluminum-based alloy sheet 12 manufactured using the process as described above can have a Yield Strength (YS) of between about 200 MPa and about 500 MPa, depending on the nature of the alloy, the thickness of the sheet, etc. Moreover, the resulting aluminum-based alloy sheet 12 can have an Ultimate Tensile Strength (UTS) of between about 220 and about 520, depending on the nature of the alloy, the thickness of the sheet, etc. Finally, the resulting aluminum-based alloy sheet 12 can have an elongation of between about 1% and about 12%, depending on the nature of the alloy, the thickness of the sheet, etc. Non-limitative examples are detailed in Table 1.

TABLE 1 Alloy Sheet Tensile Property Range for four different aluminum-based alloys AA5182 AA6005 AA6016 AA6014 UTS (MPa) 440-470 310-340 270-300 300-330 YS (MPa) 420-450 300-330 260-290 290-320 Elongation (%)  2-5  4-7  6-7  5-6 Remarks Properties Properties Properties Properties obtained obtained obtained obtained under the under the under the under the state of 0.208 state of 1 mm state of 1 mm state of 1 mm mm as rolled as rolled after as rolled after as rolled after after 90% cold 50% cold 50% cold 67% cold reduction. reduction. reduction. reduction.

Experiments And Results

The following working examples and experiments further illustrate the above-described casting process and are not intended to be limiting in any respect.

A number of experiments were conducted to assess operating parameters and performance of the process for manufacturing an aluminum-based alloy sheet directly from a molten aluminum-based alloy, by simultaneously casting and cooling a substantially solid and substantially thin aluminum-based alloy strip, and by rolling the substantially solid and substantially thin aluminum-based alloy strip to produce the aluminum-based alloy sheet, without carrying out any heat treatment step, such as homogenization, between the simultaneous casting and cooling operation and the rolling operation.

A number of experiments were also conducted to assess the mechanical properties of the produced aluminum-based alloy sheets, depending on the nature of the aluminum-based alloy, the operating parameters of the process, the as-cast thickness of the strips, the as-rolled thickness of the sheets, etc.

First off, FIG. 5 shows an optical micrograph of a cross section of an AA6005 AlMgSi alloy strip, which is as-cast and etched with 0.5% HF at the indicated magnification level. FIG. 6 shows an optical micrograph of a cross section of an AA6005 AlMgSi alloy strip having a thickness of 2 mm, which is as-cast and etched with a modified Barker's Reagent that includes boric acid to show uniformity of cross-section grain size at the indicated magnification level. FIG. 7 shows an optical micrograph showing microstructure at a surface of an AA6005 AlMgSi alloy strip having a thickness of 2 mm, which is as-cast and etched with 0.5% HF at the indicated magnification level. FIG. 8 shows an optical micrograph showing microstructure at the centreline region of an AA6005 AlMgSi alloy strip having a thickness of 2 mm, which is as-cast and etched with 0.5% HF at the indicated magnification level. Unlike other thin strips resulting from conventional casting processes, such as the Direct Chill casting process, benefiting from the substantially high cooling rate and substantially low compression force applied to the strip, the microstructure of the substantially solid aluminum-based alloy strip resulting of the present process is fairly uniform in cross-section, exhibiting slight coarsening towards the cast centreline.

Also, FIG. 9 shows a plot of the Ultimate Tensile Strength (UTS in MPa) vs. a ratio of the Ultimate Tensile Strength to the Yield Strength (UTS/YS, which is unitless or MPa/MPa) for 6 thin strip cast samples of AA6005 aluminum-based alloys. Indeed, the thin strip cast samples (i.e., the substantially solid aluminum-based alloy strips) were simultaneously cast and cooled to an as-cast gauge of 2 mm, cold-rolled to obtain an aluminum-based alloy sheet having an as-rolled gauge of 1 mm and then, tensile tested (cooling rate was 500-1200 K/second; time interval was 5-60 days; rolling force was 10-30 lbs per inch of cast strip width). For comparison, the plot of FIG. 9 also shows the UTS vs. the UTS/YS for aluminum-based alloy sheets obtained via a conventional Direct Chill process. The dotted lines show the results for the as-rolled AA6005 sheets (DC-AR, i.e. Direct Chill and As-Rolled) resulting from the Direct Chill process. The strips were cast to an as-cast gauge of 75 mm, homogenized for 6 hours at 560° C., hot rolled to an as-rolled gauge of 4 mm, cold-rolled for an as-rolled gauge of 1 mm, and tensile tested.

FIG. 10 shows a plot of the Yield Strength (YS) vs. a ratio of the Ultimate Tensile Strength to Yield Strength (UTS/YS) for 7 thin strip cast samples of AA6005 aluminum-based alloys. The thin strip cast samples were simultaneously cast and cooled to an as-cast gauge of 2 mm, cold-rolled to an as-rolled gauge of 1 mm, and tensile tested. Depending on the sample, the cooling rate was between about 500 K/s and about 1200 K/s; the time interval between the casting/cooling and the cold-rolling was between 5 and 60 days; and the rolling force was between about 2 and about 30 lbs per inch of cast strip width. For comparison, the plot of FIG. 10 also shows the YS vs. the UTS/YS for aluminum-based alloy sheets obtained via a conventional Direct Chill process. The dotted lines show the results for the as-rolled AA6005 sheets (DC-AR) resulting from the Direct Chill process. The strips were cast to an as-cast gauge of 75 mm, homogenized for 6 h at 560° C., hot-rolled to an as-rolled gauge of 4 mm, cold-rolled to an as-rolled gauge of 1 mm, and tensile tested.

FIG. 11 shows a plot of the Ultimate Tensile Strength (UTS in MPa) vs. a ratio of the Ultimate Tensile Strength to Yield Strength (UTS/YS) for T4 conditions (T4 referring to temper, which means the samples have been solutionized and quenched) for 5 thin strip cast samples of AA6005 aluminum-based alloys. The thin strip cast samples were cold-rolled to produce sheets having an as-rolled gauge of 1 mm, solutionized for 30 s at 560° C. and tensile tested. Depending on the sample, the cooling rate was between about 500 K/s and about 1200 K/s; the time interval between the casting/cooling and the cold-rolling was between 5 and 60 days; and the rolling force was between about 2 and about 30 lbs per inch of cast strip width. For comparison, the plot of FIG. 11 also shows the UTS vs. the UTS/YS for aluminum-based alloy sheets obtained via a conventional Direct Chill processes, under T4 conditions. The strips were cast to an as-cast gauge of 75 mm, homogenized for 6 h at 560° C., hot-rolled to an as-rolled gauge of 4 mm, cold-rolled to an as-rolled gauge of 1 mm, solutionized at 560° C., and tensile tested. As shown, the strengths exhibited by the thin strip cast T4 samples resulting from the present process were similar to those obtained for the samples resulting from the conventional process. That is, although no heat treatment (i.e., homogenization) was required to obtain those results, the physical properties of all samples were similar.

FIG. 12 shows a plot of the Ultimate Tensile Strength (UTS in MPa) vs. a ratio of the Ultimate Tensile Strength to Yield Strength (UTS/YS) for samples that underwent ageing. Thin strip cast samples of AA6005 were simultaneously cast and cooled to an as-cast gauge of 2 mm, cold-rolled to an as-rolled gauge of 1 mm, aged 5 hours at 180° C. and tensile tested. Depending on the sample, the cooling rate was between about 500 and about 1200 K/second; the time interval between the casting/cooling and the cold-rolling was between 5 and 60 days; and the rolling force was between about 2 and about 30 lbs per inch of cast strip width. For comparison, the plot of FIG. 12 also shows the YS vs. the UTS/YS for aluminum-based alloy sheets obtained via a conventional Direct Chill process. The dotted lines show the results for the as-rolled AA6005 sheets (DC-AR) resulting from the Direct Chill process. The strips were cast to an as-cast gauge of 75 mm, homogenized at 560° C. for 6 hours, hot-rolled to an as-rolled gauge of 4 mm, cold-rolled to an as-rolled gauge of 1 mm, solutionized at 560° C. for 30 seconds, aged 5 hours at 180° C. and tensile tested.

In brief, the aluminum-based alloy sheets resulting from the process described herein have similar mechanical properties to those of sheets of the same composition resulting from conventional processes, even though the present process provides no re-heating of the cast strip between the simultaneous casting and cooling operation and the cold-rolling operation. The sheets obtained via the present process can therefore reach the high metallurgical requirements of a plurality of industries, namely, of the transport industry, beverage container industry and the like, with a process that is saves time, energy and money.

Table 2 and FIGS. 13A to 13D show results of experiments with AA6016 alloy. Specifically, as-cast AA6016 strips of 5.25 inches width and designated thickness, were placed vertically in a furnace already at 515° C. The strips were rapidly heated for 15 minutes until reaching 500° C. They were then removed and hot rolled (at about 500° C.) to obtain an approximate 1 mm target thickness. When the strips came out of the hot mill, they were quenched per temper requirements. FIG. 13a , labelled “3 mm water”, shows results from 3 mm samples (cast 3.298) of AA6016 wherein sample strips were hot rolled at about 500° C. to about 1.1 mm and immediately quenched in water. FIG. 13b , labelled “3 mm T4P”, shows results from 3 mm samples (cast 3.298) of AA6016 wherein sample strips were hot rolled at about 500° C. to about 1.1 mm and rapidly quenched in water. They were pre-aged by soaking at 85° C. in a furnace for 8 hours. The furnace was then cooled naturally to room temperature in about 4 hours. FIG. 13c , labelled “3 mm Air”, shows results from 3 mm sample strips of AA6016 (cast 3.298) that were hot rolled at about 500° C. to about 1.1 mm thickness and subsequently left to cool to room temperature in air. It was estimated that it took about 10 minutes for the thin and narrow strips to cool to room temperature. Finally, FIG. 13d , labelled “2 mm Water”, shows results from 2 mm samples of AA6016 (cast 3.271) wherein sample strips were hot rolled at about 500° C. to about 1.0 mm and immediately quenched in water. Results are detailed in Table 2.

TABLE 2 Average Mechanical Properties for AA6016 samples Days after Tensile Yield Elongation rolling (MPa) (MPa) (%) 3 3 mm T4P 242.0 202.1 14.1 3 mm Water 243.3 207.5 11.8 3 mm Air 217.6 187.8 11.1 2 mm Water 264.4 217.6 16.8 4 3 mm T4P 238.9 200.2 13.3 3 mm Water 239.3 200.2 14.7 3 mm Air 232.6 209.0 7.8 2 mm Water 262.9 217.0 14.3 6 3 mm T4P 240.3 203.1 12.5 3 mm Water 236.3 196.0 15.4 3 mm Air 223.9 193.6 9.7 2 mm Water 268.0 219.0 14.9 9 3 mm T4P 240.8 199.6 16.3 3 mm Water 239.0 200.2 13.8 3 mm Air 220.7 193.3 8.9 2 mm Water 268.7 219.6 14.3 14 3 mm T4P 238.5 194.0 16.7 3 mm Water 243.5 204.2 13.8 3 mm Air 223.5 196.6 8.2 2 mm Water 268.1 219.5 15.4

Different tests were carried out with two different compositions of 6xxx series heat-treatable aluminum alloys as shown in Table 3. More particularly, aluminium-based sheets were manufactured with these two aluminum alloy compositions using two different casting processes: Direct casting (DC) and EEBC (see Table 3). The results, shown in Table 4, are mean results taken from 3 tests (n=3).

TABLE 3 Chemical composition of AA6xxx alloys Casting Weight % Alloy Method Si Fe Cu Mn Mg AA6005 DC 0.70 0.15 0.05 0.05 0.48 AA6005 EEBC 0.62 0.19 0.07 0.08 0.57 AA6016 EEBC 1.3 0.19 0.09 0.12 0.5

TABLE 4 Longitudinal T4P tensile properties of 1 mm AA6xxx (n = 3) Details of Tensile Yield Alloy, Casting Method, Heat Strength Strength Elongation Temper Heat Treatment Treatment (MPa) (MPa) (%) Typical as-delivered specifications >200 <130 >25 AA6005, DC, Full 560 C. for 213 103 25 T4P solutionizing  60 s AA6005, EEBC, Full 560 C. for 246 133 26 T4P solutionizing  60 s AA6005, EEBC, Pulse 560 C. for 246 133 28 T4P solutionizing  5 s “EEBC + pulse” AA6005, EEBC, Pulse 500 C. for 208 105 24 T4P solutionizing  5 s “EEBC + pulse” AA6016, EEBC, Pulse 500 C. for 250 126 28 T4P solutionizing  5 s “EEBC+pulse”

Experiment 1: DC Casting Followed by Conventional Solutionizing (Control Sample—Row 1 of Table 4)

A heat-treatable alloy, series AA6005, was Direct Chill (DC) cast as 75 mm thick slab, homogenized at 560° C. for 6 hours, hot rolled to 4 mm and subsequently cold rolled to 1 mm.

TABLE 5 Longitudinal T6P tensile properties of 1 mm AA6016 after a paint-baking simulation Casting Details of Tensile Yield Method, Heat Heat Strength Strength Elongation Alloy Treatment Treatment Temper (MPa) (MPa) (%) Typical paint-baked specifications T6×/T8× >240 <200 >18 AA6016 EEBC, Pulse 500° C. for T6P 302 231 20 solutionizing 5 secs (“EEBC + pulse”) (Paint-baked)

Experiment 2: EEBC Casting Followed by Conventional Solutionizing (Row 2 of Table 4)

Heat-treatable strips of AA6005 were produced via the continuous casting EEBC process, as described herein. Each strip was cast to 2 mm at a speed of 90 m/min. For AA6005, a compression force of about 50 pounds per linear inch width was applied. Each strip was immediately quenched by water inline to a room temperature in order to avoid precipitation of Mg₂Si out of solid solution. After each strip was cooled to ambient temperature, it was laboratory cold rolled from 2 mm to 1 mm at room temperature with the strip reaching a temperature not exceeding 60° C. All materials at 1 mm were subjected to a conventional solutionizing treatment with a heating time of about 60 seconds at a temperature of about 560° C.).

TABLE 6 Chemical composition of EEBC produced AA5182 strip Casting Weight % Alloy Method Si Fe Cu Mn Mg AA5182 EEBC 0.13 0.09 0.01 0.34 4.05

Experiment 3: EEBC Casting Followed by Pulse Solutionizing (“EEBC+Pulse”) (Row 3 of Table 4)

Heat-treatable strips of AA6005 were produced via the continuous casting EEBC process, as described herein with a compression force of about 50 pounds per linear inch width. Each strip was cast to 2 mm at a speed of 90 m/min. Each strip was immediately quenched by water inline to a room temperature in order to avoid precipitation of Mg₂Si out of solid solution. After the strip was cooled, it was cold rolled to 1 mm. All materials at 1 mm were subjected to a pulse solutionizing treatment with a heating time of about 3 to about 10 seconds at a temperature of about 560° C.

Experiment 4: EEBC Casting Followed by Lower Temperature Pulse Solutionizing (“EEBC+Pulse”) (Row 4 of Table 4)

Heat-treatable strips of AA6005 were produced via the continuous casting EEBC process, as described herein with a compression force of about 50 pounds per linear inch width. Each strip was cast to 2 mm at a speed of 90 m/min. Each strip was immediately quenched by water inline to a room temperature in order to avoid precipitation of Mg₂Si out of solid solution. After the strip was cooled, it was cold rolled to 1 mm. All materials at 1 mm were subjected to a pulse solutionizing treatment with a heating time of about 3 to about 10 seconds at a temperature of about 500° C.

Experiment 5: EEBC Casting Followed by Lower Pulse Solutionizing (“EEBC+Pulse”) (Row 5 of Table 4)

Heat-treatable strips of AA6016 were produced via the continuous casting EEBC process, as described herein with a compression force of about 60 pounds per linear inch width. Each strip was cast to 2 mm at a speed of 90 m/min. Each strip was immediately quenched by water inline to a room temperature in order to avoid precipitation of Mg₂Si out of solid solution. After the strip was cooled, it was cold rolled to 1 mm. All materials at 1 mm were subjected to a pulse solutionizing treatment with a heating time of about 3 to about 10 seconds at a temperature of about 500° C.

Pulse solutionizing was conducted by immersing a strip in a molten salt-bath for various short soaking durations, typically about 1 to about 10 seconds. During this time, samples were rapidly heated to a target temperature in the range of 500° C. to 560° C. Once this temperature range was reached, samples were immediately removed from the salt bath and quenched in cold water. The strip temperature during immersion in the molten salt-bath was measured by a thermocouple embedded in the strip and the recorded data were data logged.

Immediately after quenching, all samples underwent a T4P treatment at 85° C. for a total soak of 8 hours. Samples treated in this way are considered to have a T4P temper. This heat-treatment is a recognized laboratory practice meant to simulate a pre-age. The aim of pre-ageing is to stabilize microstructure (e.g., clusters and zones) such that strength loss is reduced, or even eliminated, during subsequent natural ageing. The T4P treatment should not produce any significant increase in the initial strength, which is important for the formability needed for automotive body-panel applications.

Finally, tensile samples were machined and tested in the rolling direction after a minimum of 7 days of natural ageing. Results are shown in Table 4 and explained below.

First, a comparison was conducted between Direct Chill conventional casting versus EEBC casting for AA6005 sheets, as shown in row 1 versus row 2. The EEBC casted sheet exhibited higher T4P strength values compared to the Direct Chill cast alloy, which could be the result of the retention of higher amounts of Mg₂Si in solid solution after solutionization.

A comparison was also conducted between EEBC casts of AA6005 that were conventionally solutionized (i.e, 60 seconds at 560° C.) versus EEBC+Pulse casts (i.e., the casting process was EEBC and the solutionizing was performed by a pulse heating step (i.e, 5 seconds at 560° C.)), as shown in row 2 versus row 3 of Table 4. Mechanical properties, including strength and ductility, were equivalent for the conventionally solutionized EEBC samples as for the EEBC+Pulse samples, with EEBC+Pulse requiring a lower energy consumption and thus being . Thus, Equivalent mechanical properties of these samples was demonstrated even though there is a significant difference between the energy efficiency and thus lower processing/operating costs.

The effect of the temperature of solutionization was also investigated for the EEBC+Pulse treatment of AA6005, as shown in row 1, row 3, and row 4 of Table 4. For a lower temperature, a temperature of about 500° C. was selected. As expected, lower mechanical properties were obtained for a temperature of solutionization of 500° C. (row 4) versus a temperature of solutionization of 560° C. (row 3). However, the mechanical properties of the AA6005 solutionizing by pulse solutionizing at 500° C. (row 4) are equivalent to those of the conventionally cast Direct Chill samples of AA6005 with a conventional solutionizing of 560° C. shown in row 1 of Table 4, which is a surprising result since the lower solutionizing temperature (i.e, 500° C.) would not be used for conventional solutionizing. More particularly, conventional solutionizing at 500° C. would be expected to produce an AA6005 product that falls significantly short of these values. Notably, the equivalent mechanical properties for these two test results demonstrate the value of the EEBC+Pulse process for providing substantially equivalent products, in term of mechanical properties, from less energy consumption and thus lower processing/operating costs.

The effect of the composition of the aluminum alloy was also investigated, as shown in rows 4 vs 5 of Table 4, for the EEBC+Pulse treatment (5 seconds at 500° C.). More particularly, the mechanical properties of the AA6016 alloy following the EEBC+Pulse treatment (row 5) were compared to those of the AA6005 alloy (row 4). AA6016 alloy is characterized by a higher concentration of Mg and Si than AA6005 alloy. As shown in rows 4 and 5, the yield strength and elongation of both aluminum alloys after the low-temperature pulse treatment were sufficient to satisfy the industry standards. Thus, the results showed in Table 4 demonstrate that the cast and rolled aluminum alloys treated with the EEBC+Pulse process were fully solutionized using the above-described cost effective, low-temperature and shorter-duration practice, and met the T4 specifications.

The samples produced via the above-detailed examples were additionally examined for grain size. More particularly, FIGS. 14A, 14B, and 14C show optical micrographs of cross sections of AA6005 AlMgSi alloy strip having a thickness of 1 mm, which respectively underwent pulse solutionizing at 500° C. for 5 seconds (Table 3, row 4), pulse solutionizing at 560° C. for 5 seconds (Table 3, row 3), and conventional solutionizing at 560° C. for 60 seconds (Table 3, row 1). The EEBC+Pulse processing (5 sec 500° C. and 560° C.) produced fully recrystallized grains in the range of about 20 μm to about 30 μm. A simulation of the conventional solutionizing heat treatment (60 seconds at 560° C.) produced grains in the range of about 40 μm to about 50. It is known that a finer grain size increases the material's ductility and is beneficial, if not critical, to the forming of an auto-body panel. Thus, the optical micrographs of FIGS. 14a and 14b demonstrate that the EEBC+Pulse process produced aluminum alloy strips with superior mechanical properties in comparison with the aluminum alloy strips processed.

After an automotive closure part (e.g., body panel) is formed, it is typically subjected to thermal treatments as the paints and lacquers are cured. To simulate this ‘paint-baking’ processes in the laboratory, samples were placed in an air-circulating muffle furnace held at 180° C. for 30 minutes. After this treatment, samples were considered to be in the artificially age-hardened T6 temper. As can be seen from Table 5, the T6 paint-baked or age-hardened properties of the EEBC+Pulse AA6016 alloy (5 sec, 500° C.), exceeded properties attained for conventional processed AA6016. It will be appreciated that these improved properties of ultimate tensile strength, yield strength and elongation of the strip reached by the EEBC+Pulse processing produced an aluminum alloy sheet that was superior to the aluminum alloy sheet produced from previously known methods.

Experiment 2: Testing of Non-heat Treatable Alloy

In the following example, a non-heat treatable alloy AA5182, with the chemical composition given in Table 6, was produced via the EECB process, as described herein. The strip was cast at 2 mm with a compression force of about 75 pounds per linear inch width, cold rolled from 2 mm to 1 mm and then pulse annealed at 510° C. for 10 seconds in a molten salt bath as described above to produce an O-tempered material. The cold rolling was performed in laboratory at room temperature with the strip reaching a temperature not exceeding 80° C. As a comparison, a 1 mm AA5182 sheet cold rolled from 2 mm EECB strip was subject to a simulation of a conventional batch annealing process at 380° C. for 2 hours in an air-circulating muffle furnace. Samples were then prepared for longitudinal tensile testing and the results are shown in Table 7. The samples were also metallographically examined for grain size determination.

TABLE 7 Tensile properties of 1 mm AA5182 sheet under various processing Tensile Yield Casting Heat Strength Strength Elongation Alloy Method Treatment Temper (MPa) (MPa) (%) AA5182 EEBC Batch O 289 139 25.0 annealing: 380° C. for 2 hours AA5182 EEBC Pulse O 286 130 26.1 annealing: 510° C. for 10 seconds

As shown in FIG. 15A, the grain structure of 1 mm AA5182 cold rolled sheet was fully recrystallized after pulse annealing at 510 C. Pulse annealing produced uniform and equiaxed grains, with a mean grain size of around 20 μm. In comparison, and as shown in FIG. 15B, the grains of the AA5182 strip produced via conventional batch annealing were significantly coarser, not nearly as uniform, and had a mean grain size of about 40 μm. The uniformity and small grain size is an extremely desirable property for O-temper automotive structural applications. Structural panels of a monocoque auto-body have fairly modest requirements in terms of strength (most designs utilize relatively thick gauges to provide sufficient stiffness), but require a high degree of formability (elongation) in order to produce the complex shapes required. As shown in Table 7, tensile properties of 1 mm AA5182 sheet after pulse annealing are comparable to those produced via batch annealing. Pulse annealing at 510 C for 10 seconds generated slightly higher elongation, which can be partly attributed to the significantly finer grains observed in the microstructure. Notably, the combination of EECB processing followed by pulse annealing (EEBC+Pulse) gave superior elongation values, and more uniform and finer grain structure when compared with the previously known methods, including conventional batch annealing.

Although the present invention has been described hereinabove by way of specific embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention defined in the appended claims.

In the present description, the same numerical references refer to similar elements. Furthermore, for the sake of simplicity and clarity, namely so as to not unduly burden the figures with several reference numbers, not all figures contain references to all the components and features, and references to some components and features may be found in only one figure, and components and features of the present disclosure which are illustrated in other figures can be easily inferred therefrom. The embodiments, geometrical configurations, materials mentioned and/or dimensions shown in the figures or described in the present disclosure are embodiments only, given solely for exemplification purposes.

Moreover, steps of the process(es) described herein could be modified, simplified, altered, omitted and/or interchanged, without departing from the scope of the present disclosure, depending on the particular applications which the present process is intended for, and the desired end results, as briefly exemplified herein and as also apparent to a person skilled in the art.

Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment.

Reference in the specification to “some embodiments”, “an embodiment”, “one embodiment” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the inventions. It is to be understood that the terms “including”, “comprising”, “consisting” and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps or integers.

It is to be understood that where the claims or specification refer to “a” or “an” element, such reference is not be construed that there is only one of that element. It is to be understood that where the specification states that a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included.

The descriptions, examples, methods and materials presented in the claims and the specification are not to be construed as limiting but rather as illustrative only. The present invention may be implemented in the testing or practice with methods and materials equivalent or similar to those described herein.

In the following description, the term “about” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e. the limitations of the measurement system. It is commonly accepted that a 10% precision measure is acceptable and encompasses the term “about”.

Several alternative embodiments and examples have been described and illustrated herein. The embodiments of the invention described above are intended to be exemplary only. A person of ordinary skill in the art would appreciate the features of the individual embodiments, and the possible combinations and variations of the components. A person of ordinary skill in the art would further appreciate that any of the embodiments could be provided in any combination with the other embodiments disclosed herein. It is understood that the invention may be embodied in other specific forms without departing from the central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. Accordingly, while the specific embodiments have been illustrated and described, numerous modifications come to mind. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims. 

1. A process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy, the process comprising: continuously casting and simultaneously cooling an aluminum-based alloy strip thinner than about 10 mm by feeding a belt caster with the molten aluminum-based alloy, with a compression force on the aluminum-based alloy strip, during its solidification, in a range of about 2 to about 3000 pounds per linear inch of alloy strip width to obtain the aluminum-based alloy strip in a substantially solid state.
 2. A process for manufacturing an aluminum-based alloy sheet from a molten aluminum-based alloy, the process comprising, in a continuous in-line sequence: continuously casting and simultaneously cooling the molten aluminum-based alloy to obtain an aluminum-based alloy strip thinner than about 10 mm, while applying a compression force on the aluminum-based alloy strip, during its solidification, in a range of about 2 to about 3000 pounds per linear inch of alloy strip width to obtain the aluminum-based alloy strip in a substantially solid state.
 3. The process of claim 1, further comprising rolling the substantially solid aluminum-based alloy strip following the simultaneous casting and cooling to obtain the aluminum-based alloy sheet.
 4. The process of claim 1, wherein the compression force applied on the solidifying aluminum-based alloy strip ranges between about 10 to about 150 pounds per linear inch of alloy strip width. 5-7. (canceled)
 8. The process of claim 1, wherein the simultaneous casting and cooling is carried out with a belt caster.
 9. The process of claim 3, further comprising quenching the substantially solid aluminum-based alloy strip following the simultaneous casting and cooling and prior to the rolling.
 10. The process of claim 9, wherein the process is free of heat treatment step following the simultaneous casting and cooling and prior to the rolling.
 11. The process of claim 3, wherein the process is free of quenching and heat treatment steps following the simultaneous casting and cooling and prior to the rolling, to obtain the aluminum-based alloy sheet.
 12. The process of claim 3, further comprising quenching the aluminum-based alloy sheet following the rolling.
 13. The process of claim 12, further comprising artificially ageing the aluminum-based alloy sheet following the quench.
 14. The process of claim 3, further comprising artificially ageing the aluminum-based alloy sheet following the rolling.
 15. The process of claim 1, wherein the simultaneously cooling is performed at a cooling rate of between about 100 K/s and about 1500 K/s.
 16. The process of claim 3, wherein the rolling comprises cold-rolling at a temperature in a range of about room temperature to about 150° C.
 17. (canceled)
 18. The process of claim 3, further comprising coiling the aluminum-based alloy strip following the simultaneously casting and cooling and uncoiling the coiled aluminum-based alloy strip before rolling the aluminum-based alloy strip. 19-46. (canceled)
 47. The process of claim 1, further comprising pulse heating the aluminum-based alloy strip at a temperature range of about 400° C. to about 570° C. for a time period in a range of about 2 seconds to about 10 seconds. 48-56. (canceled)
 57. An aluminum-based alloy sheet manufactured using the process of claim 1, having a yield strength of between about 200 MPa and about 500 MPa, an ultimate tensile strength of between about 220 MPa and about 520 Mpa, and an elongation of between about 1% and about 12%. 58-61. (canceled)
 62. The process of claim 2, further comprising rolling the substantially solid aluminum-based alloy strip following the simultaneous casting and cooling to obtain the aluminum-based alloy sheet.
 63. The process of claim 2, wherein the compression force applied on the solidifying aluminum-based alloy strip ranges between about 10 to about 150 pounds per linear inch of alloy strip width.
 64. The process of claim 2, wherein the simultaneous casting and cooling is carried out with a belt caster and the rolling comprises cold-rolling performed at a temperature in a range of about room temperature to about 150° C.
 65. The process of claim 2, wherein the simultaneously cooling is performed at a cooling rate of between about 100 K/s and about 1500 K/s.
 66. The process of claim 2, further comprising pulse heating the aluminum-based alloy strip at a temperature range of about 400° C. to about 570° C. and for a time period in a range of about 2 seconds to about 10 seconds.
 67. An aluminum-based alloy sheet manufactured using the process of claim 2, having a yield strength of between about 200 MPa and about 500 MPa, an ultimate tensile strength of between about 220 MPa and about 520 Mpa, and an elongation of between about 1% and about 12%. 